AHMEDABAD: The discharge of untreated toxic effluents and sewage into the state’s rivers is taking a toll on the purity of these invaluable sources of water. One of the country’s most comprehensive surveys covering 16 river basins carried out to measure toxic metal content in Indian rivers, has detected metal content above permitted limits in Sabarmati, Tapi, Narmada, Damanganga and Purna rivers and river basins of the state.

The survey that was carried out by the water quality monitoring network of the Central Water Commission (CWC), spanned three years. According to its findings, of the nine toxic metals, metal salts of copper, iron, lead and nickel have been detected in Gujarat’s river basins above permissible limits.

For instance, the CWC found that the copper content in Sabarmati at a place downstream like Vautha was 62% higher than the permissible limit of 50 microgram per litre. Similarly the iron content was found to be 895 microgram a litre when ideally it should have been three times lower at 300 microgram a litre. At Burhanpur in the Tapi basin, for instance, the CWC found the presence of iron to be 11 times higher than the permissible limit. At the same place, even the presence of copper metal was over permissible limits.

The survey report blames flawed mining processes, discharge of industrial effluents containing metallic solutions, dumping of solid wastes which contain metal salts and some agricultural practices such as the use of metal-based biocides for the high toxicity of the river waters. The other culprits responsible for the pollution are battery manufacturing industries, paint manufacturing units, electroplating units, viscous-rayon manufacturing industries, copper picking units and galvanizing and rubber processing industries. All these produce effluents that contain high amounts of heavy metals.

A senior GPCB official said Vatva, Naroda and Narol areas are principally responsible for the discharge of chemical effluents in the Sabarmati. “We are keeping watch and have managed to curb this menace to a degree,” said the official.

The metals considered toxic are lead, arsenic, copper, cadmium, mercury and nickel. Contamination of river water with toxic metals makes it harmful for further use not only for drinking purposes but also by industries. In particular, arsenic and lead make the water dangerous to drink.

These toxic metals are reported to cause chromosomal damage and lead to hereditary ailments. The report further says that an 80 microgram/dL arsenic concentration in human blood cause poisoning in adults. It has also been reported that lead concentrations above 40 microgram/dL in the blood causes brain damage in children.

Chief engineer, CWC, M P Singh says storm water runoff and discharge of sewage into rivers are two common ways that pollutants enter the aquatic ecosystems resulting in pollution. “The heavy metals are highly persistent and have the potential to bio-accumulate and bio-magnify in the food chain and become toxic for living organisms at higher tropic levels in nature,” says Singh.